1. Field of the Invention
The present invention relates to a differential apparatus, and more specifically to an improvement for lubrication of a differential apparatus composed of parallel axis pinion gears which and which is applicable to front, center and rear differential gears for an automotive vehicle.
2. Description of the Prior Art
Some examples of prior art differential apparatus related to a first aspect of the present invention will he described hereinbelow with reference to the attached drawings.
FIG. 1 shows a first prior art differential apparatus disclosed in Japanese Published Unexamined (Kokai) Utility Model Application No. 1-146062. This differential apparatus 201 includes a plurality of worm wheel sets 209 each composed of two worm wheels 207 separately in mesh with a respective other at each spur gear portion thereof and a pair of worm gears 211 and 213 (i.e., side gears) each in mesh with each worm wheel 207, each of the two worm gears 211 and 213 are spline-coupled with one of two output (wheel drive) shafts 215 and 217 of an automotive vehicle, respectively.
Therefore, when a differential casing 219 is rotated by an engine power, the drive power of the engine is distributed to both right and left output (wheel drive) shafts from the worm wheel sets 209 to the two worm gears (i.e., two side gears) 211 and 213, respectively. In this case, the differential motion can be limited by frictional resistances generated between the worm wheels 207 and worm gears 211 and 213, respectively.
FIG. 2 shows a second prior art differential apparatus whose structure is similar to that disclosed in Japanese Published Unexamined (Kokai) Patent Application No. 6-207645. This differential apparatus 203 includes a pair of helical pinion gears 221 and 223 slidably and rotatably housed in accommodation holes formed in a differential casing, respectively and in mesh with each other. A pair of helical side gears 225 and 227 are in mesh with the helical pinion gears 223 and 221, respectively. Further, the helical side gears 225 and 227 are spline-coupled with one of two output (wheel drive) shafts of an automotive vehicle, respectively.
Therefore, when a differential casing is rotated by an engine power, the drive power of the engine is distributed to both right and left wheels from the helical pinion gears 221 and 223 to the helical side gears 225 and 227, respectively. In this case, the differential motion can be limited by frictional resistances generated between the respective helical gears 221, 223, 225 and 227 due to thrust forces generated by gearing between the respective helical gears. The differential motion can also be limited by other frictional resistance generated between the respective helical gears 221, 223, 225 and 227 and the inner wall surfaces of accommodation holes or sliding portions of the differential casing due to reaction forces generated between the respective helical gears. In the differential apparatus 203, the two helical side gears 225 and 227 are directly in sliding contact with respect to each other at each inner end surface thereof.
FIG. 3 shows a third prior art differential apparatus disclosed in Japanese Published Unexamined (Kokai) Patent Application No. 7-71560. This differential apparatus 205 includes two helical side gears 229 and 231 and a thrust washer 233 interposed between the two side gears 229 and 231. In this differential apparatus 205, the two helical side gears 229 and 231 are indirectly slid with respect to each other via the thrust washer 233.
In order to obtain a stable differential limiting force generated due to the sliding motion between the two helical side gears 229 and 231; that is, to prevent the vibration of the two helical side gears, the helical side gear 229 is formed with a cylindrical projected portion 235 and the helical side gear 231 is formed with a cylindrical recessed portion 237 so that the two helical side gears can be aligned with each other at a centering portion 239. In addition, a thrust block 241 is interposed between two inner circumferential surface portions of the two helical side gears 229 and 231 in such a way as to be brought into contact with the inner ends of the two output shafts fixed to the two side gears 229 and 231, respectively.
In the above-mentioned first prior art differential apparatus shown in FIG. 1, a helical oil groove 243 is formed in the differential casing 219 for lubrication. Further, in the differential apparatus shown in FIG. 3, in general, some oil gaps (i.e., grooves) are formed by cutting off some teeth formed at the spline portion between each helical side gear 229 or 231 and each output shaft, in order to introduce lubricant from the helical oil groove (e.g., as shown in FIG. 1) into an inner side between the two helical side gears 229 and 231. In other words, in the differential apparatus, although some oil passages are generally formed to introduce lubricant from outside differential casing to the inside the differential casing, when the thrust block 241 is interposed in the inner circumferential surface portions of the two helical side gears 229 and 231 as shown in FIG. 3, since lubricant flow is shut off by the presence of the thrust block 241. It is difficult to allow the introduced lubricant to flow to the respective sliding portions between the thrust block 241 and the two inner end surfaces of the two helical side gears 229 and 231. Thus, there exists a problem in that seizure occurs at the inner end surfaces of the two helical side gears 229 and 231. In addition, the centering portion 239 as shown in FIG. 3. Prevents the lubricant from flowing smoothly, and there exists another problem in that seizure occurs at the sliding portion at this centering portion 239.
In addition, once lubricant flow is shut off as described above, lubricant cannot flow smoothly through the gaps formed between the helical side gears 229 and 231 and the output shafts respectively, there arises anther problem in that cracks are easily produced due to the fretting corrosion at the spline portions between the side gears and the output shafts, respectively.
In addition, when the centering portion 239 is formed as shown in FIG. 3, the two helical side gears 229 and 231 cannot be used in common, and there exists a disadvantage that the number of parts increases that is, a single type gear cannot be utilized.
An example of prior art differential apparatus related to a second aspect of the present invention will be described hereinbelow with reference to the attached drawings.
FIGS. 4(a) and 4(b) show a fourth prior art differential apparatus disclosed in Japanese Published Unexamined (Kokai) Patent Application No. 6-207646. This differential apparatus is of parallel shaft type, in which a differential limiting force can be obtained by rotational frictional forces generated between pinion gears and two side gears.
In the differential apparatus 401 shown in FIG. 4(a), a pair of side gears 404 and 406 are rotatably disposed in a differential casing 402 coaxially with the casing 402 so as to oppose each other at the central portion of the casing 402. Further, the two side gears 404 and 406 are aligned with each other at a centering portion 405 by butting an inner projecting end surface of the side gear 404 into an inner recessed end portion of the side gear 406.
Further, a plurality of pairs of pinion gears 408 are arranged within the differential casing 401 in parallel with and around the rotational axis of the two side gears 404 and 406. One of the two pinion gears of each pair is in mesh with the left side gear 404 and the other (not shown) of the two pinion gears of each pair is in mesh with the right side gear 406. Further, the two pinion gears 408 in each pair are in mesh with each other.
The differential casing 402 is formed with accommodation holes 410 for housing these pinion gears 408 respectively, so that each of pinion gears 408 is slidably and rotatably housed in one of these accommodation holes 410. Further, the differential casing 402 is formed with a lubricant opening 412 in the outer circumferential wall thereof to exhaust lubricant from the rotating pinion gears 408 to the outside of the differential casing 402.
Therefore, when the differential casing 402 is rotated, an engine power is distributed from the pinion gears 408 to the two side gears 404 and 406; and then to the two output shafts, respectively. In more detail, the engine power can be distributed differentially to the right and left wheels, respectively on the basis of rotations of the respective pinion gears 408 each rotating on its own axis according to a difference in drive resistance between the two wheels. In this case, since the pinion gears 408 are slidably rotating in the accommodation holes 410 formed in the differential casing 402, respectively, once a differential motion occurs, a differential limiting force can be obtained due to the frictional resistances generated between the respective pinion gears 408, the side gears 404 and 406 and the other members (e.g., inner wall surfaces of the differential casing) in contact with these gears.
In the differential apparatus shown in FIG. 4(a), it is effective to provide a centering portion 405 between two inner end surfaces of the two side gears 404 and 406, in order to prevent misalignment between each pinion gear 408 and the center of each accommodation hole 41. This feature stabilizes the differential limiting characteristics, without causing any seizure between each pinion gear 408 and each accommodation hole 410.
Further, in the differential apparatus 401 of this type, it is well known that frictional force can be increased and thereby the differential limiting force can be strengthened by constructing the respective gears 404, 406 and 408 as helical gears; that is, by sliding the outer end surface portions 414 and 418 of the two side gears 404 and 406 with inner wall surfaces of the differential casing 402 according to the drive torque inputted to the differential casing 402, and by sliding the inner end surfaces 416 of the two side gears 404 and 406 with each other. Here, it is preferable to interpose a washer at each of these sliding portions 414, 416 and 418 to prevent the end surfaces of the side gears 404 and 406 and the wall surface of the differential casing 402 from being worn off easily, to eliminate the heat treatment process, and to smoothen the slidable motion for stabilization of the differential limiting characteristics, as disclosed in Japanese Published Unexamined Patent Application Nos. 6-1017414, and 6-185581.
However, in the prior art differential apparatus as shown in FIG. 4(a), since the boss portions of the two side gears 404 and 406 are formed into cylindrical shape, respectively, lubricant flows into the inner space formed between the two end surfaces of the two side gears through oil gaps formed by cutting off some teeth of each spline portion between the inner circumferential surface of the side gear and the outer circumferential surface of the output shaft, respectively, as shown by arrows shown in FIG. 4(b).
In the prior art differential apparatus shown in FIG. 4(a), however, the inner space formed between the two end surfaces of the two side gears 404 and 406 is closed by the fitting surface at the centering portion 405 between the two side gears 404 and 406, and the lubricant entering the inner space between the two side gears 404 and 406 cannot flow radially outward to the outer circumferential surfaces of the boss portion of the two side gears 406. Thus, there exists a problem in that lubricant cannot flow smoothly. In other words, at the centering portion 405, both the side gears are aligned with each other by bringing the two circumferential fitting surfaces of both the side gears into sliding contact with each other. The sliding contact portions shut off enclose the lubricant passage so that it has been impossible to obtain a definite lubricant flow.
Further, in the case where other boss portions are formed on the side of the axially outer end surfaces 414 and 418 of the side gears 404 and 406 in order to form two centering portions for the two side gears by use of the inner wall surfaces of the differential casing 402, the lubricant passage is blocked, and a definite lubricant flow cannot be obtained.
Some examples of prior art differential apparatus related to a third aspect of the present invention will be described hereinbelow with reference to the attached drawings.
FIG. 5 shows a fifth prior art differential apparatus disclosed in Japanese Published Unexamined (Kokai) Patent Application No. 59-97346. In this differential apparatus 501, a differential casing 503 is composed of a casing body 503a and two casing covers 503b and 503c. Engine power for rotating the differential casing 503 is transmitted from three pairs of first and second pinion gears 505 and 507 to two output shafts via two right and left side gears 509 and 511. The first and second pinion gears 505 and 507 and the right and left side gears 509 and 511 are all spur gears. Further, each pair of pinion gears 505 and 507 are slidably and rotatably housed in a respective of accommodation holes 513 and 515 formed in the casing body 503a of the differential casing 503.
When an engine torque is transmitted to the output shafts during straight drive or turning drive, the two pinion gears 505 and 507 are brought into pressure contact with the wall surfaces of the accommodation holes 513 and 515. This is due to the gearing between the two pinion gears 505 and 507 and the two side gears 509 and 511, respectively or due to the gearing between the two pinion gears 505 and 507 themselves pinion gears 505 and 507 rotate under frictional contact with the differential casing 503. The frictional resistance generated as described above becomes a differential limiting force for the differential apparatus.
FIG. 6 shows a sixth prior art differential apparatus disclosed in Japanese Published Unexamined (Kokai) Patent Application No. 60-175843. In differential apparatus 601, a drive power of an engine for rotating a differential casing 603 is transmitted from pairs of two pinion gears 605 and 607 to the two output shafts via two output side gears 609 and 611, respectively. These pinon gears 605 and 607 are also slidably and rotatably housed in accommodation holes 613 and 615 formed in the differential casing 603, respectively. The pinion gears 605 and 607 and the side gears 609 and 611 are all helical gears. Further, the differential casing 603 is formed with an opening 619 on a side wall portion thereof to introduce lubricant from outside thereof into the differential casing 603.
When a torque is being transmitted, the helical pinion gears 605 and 607 are brought into pressure contact with the wall surfaces of the accommodation holes 613 and 615 of the differential casing 603, respectively by reaction force generated due to the gearing between the helical pinion gears and the helical side gears respectively, and frictional forces can thus be generated thereat. Further, other frictional forces can be also generated between the helical side gears 609 and 611 and between the respective helical gears 605, 607, 609 and 611 and the inner wall surfaces of the differential casing 603 due to thrust forces generated by the gearing between the helical gears. The frictional resistance generated as described above becomes a differential limiting force of the differential apparatus.
FIGS. 7(a) and 7(b) show a seventh prior art differential apparatus disclosed in Japanese Published Unexamined (Kokai) Patent Application No. 6-323373. In this differential apparatus 701, a drive power of an engine for rotating a differential casing 704 composed of a differential body 702 and a cover 703 is transmitted from a plurality (three in this example) of pairs of pinion gears 705 and 707 in mesh with each other. These pinion gears belong to central pinion gears of different pairs, respectively. Drive is transmitted to two output shafts via two right and left side gears 709 and 711, respectively. These pinon gears 705 and 707 are also slidably and rotatably housed in accommodation holes 713 and 715 formed in the differential casing 703, respectively. The pinion gears 705 and 707 and the side gears 709 and 711 are all helical gears. Further, the differential casing 703 is formed with an opening 720 on the outer circumferential wall portion of the casing body 702 to communicate with the outside of the differential casing 704.
When torque is being transmitted, the pinion gears 705 and 707 are brought into pressure contact with the wall surfaces of the accommodation holes 713 and 715 of the casing body 702, respectively by reaction force generated due to the gearing between the pinion gears and the side gears, respectively, and thus frictional forces can be generated thereat. Further, other frictional forces can be also generated between side gears 709 and 711 and between the respective gears 705, 707, 709 and 711 and the differential casing 704 due to thrust force generated by the gearing between the respective helical gears. The frictional resistance generated as described above becomes a differential limiting force of the differential apparatus.
In the above-mentioned prior art differential apparatus 501, 601 and 701 as shown in FIGS. 5, 6, and 7(a) and 7(b), the differential limiting force can be obtained by the respective gearing reaction forces generated between the pinion gears and the side gears according to the input torque and on the basis of the frictional resistance generated between the pinion and side gears and the differential casing due to the gearing thrust force. Accordingly, when sufficient lubricant is not supplied into the differential casing, that is, to the sliding portions between the pinion gears 505 and 507; 605 and 607; 705 and 707 and the accommodation holes 513 and 515; 613 and 615; and 713 and 715, respectively, there arises a serious problem in that seizure and scuffing (gall) occur. The result is that a stable differential limiting force cannot be obtained.
In particular, as with the case of the differential apparatus 601 and 701 as shown in FIGS. 6, 7(a) and 7(b), when the side gears 609 and 611; and 709 and 711 and the pinion gears 605 and 607; and 705 and 707 are helical gears, since the frictional forces generated at the end surfaces of the pinion gears and the side gears due to the above-mentioned thrust force contributes much to the differential limiting force. Sufficient lubrication is particularly essential at the respective end surfaces of these gear elements. It has been impossible to obtain sufficient lubrication by introducing lubricant only through the opening 619 or 720 formed in the side wall or the outer circumferential wall of the differential casing. This is because when lubricant is introduced into the differential casing through the opening 619 or 720, the introduced lubricant is scattered rearward and outward by centrifugal force of the various gears. Thus, lubrication effect is particularly small at the sliding portions between the end surfaces of the side gears and the differential casing and at the sliding portions between the end surfaces of the pinion gears and the differential casing. Thus, there arises a serious problem in that seizure and scuffing occur frequently at these sliding portions, with the result that a stable differential limiting force cannot be so far obtained.